In the design of transmissions, particularly heavy duty transmissions such as used on trucks, there has existed for a long time the problem of shifting the transmission through the various speed ratios, which problem is even greater when the transmission is provided with an auxiliary or range transmission section for increasing the number of speed ratios. In most known transmissions, the shifting process is either relatively difficult and/or the shifting mechanism is relatively complex. Thus, there has been a continuing effort in the design of transmissions to improve the shifting, to improve the rapidity of shifting, to reduce the complexity of the shifting mechanism and to reduce its cost. Hence, without detracting from the operability or desirability of many of the shifting mechanisms previously known, it may be stated that in the present invention these general objectives are accomplished to even a greater degree than has been previously known.
Particularly, most known transmissions have necessarily utilized synchronizers, of which many different types are known, for causing the speed of the jaw or toothed clutch members to be substantially synchronized prior to permitting their interengagement during a shifting sequence from one speed ratio to another speed ratio. While the use of synchronizers does permit the shifting operation to be performed, nevertheless the use of synchronizers is, in many instances, undesirable since not only do synchronizers increase the mechanical complexity of the transmission, but they also occupy additional space so that the transmission is necessarily larger and heavier and is likewise of increased cost. The synchronizers also undergo substantial wear and thus require periodic maintenance. Accordingly, there has long existed a need for a successful heavy duty transmission which can be successfully operated for long periods of time without requiring the use of conventional synchronizers and yet one which will permit successful and simple shifting thereof.
A further disadvantage of many known transmissions, including those utilizing conventional synchronizers, is the large amount of effort or force which must be exerted by the vehicle driver in order to successfully shift from one speed ratio to another. The shifting operation in such known transmissions generally requires that the operator apply a force through a shifting linkage so as to move one jaw clutch member axially into meshing engagement with another jaw clutch member. Further, the force which must be exerted by the driver to perform the shifting is often of a substantial magnitude. The necessity of exerting such effort to permit the shifting operation to be performed is obviously undesirable since under conditions of frequent shifting, such as heavy traffic or mountain driving, it may be extremely tiring for the driver.
Still another disadvantage of the shifting mechanisms of known transmissions is the length of time required for the shifting operation to be performed. Most known transmissions, due to the necessity of having synchronizers and other related structure, have necessarily provided a substantial amount of mass on the main transmission shaft. Such mass considerably increases the inertia of the transmission main shaft so that a synchronized speed condition can be rapidly achieved only by the use of large synchronizers. This results in still further size and expense.
Further, in transmissions provided with a range or auxiliary section, the above problems are even more difficult and complex. Particularly when the auxiliary transmission is set to produce a first range of speeds, the speed of the engine must be altered to a predetermined extent to shift the main transmission section from one ratio to the next. However, when the auxiliary transmission is set to produce a second range of speeds, the engine speed must be altered a different amount in order to shift the gears in the main transmission. Thus, when it is necessary to make both a range and a main transmission shift, driving of the vehicle with many of the known transmissions has been difficult since it has required either a complex control mechanism or a conscious and physical effort by the driver to shift through the two ranges of speed.
Accordingly, it is an object of the present invention to provide a transmission having an improved shifting structure for overcoming the above-mentioned disadvantages. Particularly, it is an object of the present invention to provide:
1. A transmission having means to improve the ease of shifting, to improve the rapidity of shifting without requiring large synchronizers, to reduce the complexity of the mechanism and to reduce its cost.
2. A transmission, as aforesaid, having a shifting mechanism which does not require the use of conventional synchronizers.
3. A transmission, as aforesaid, which utilizes resilient means for causing meshing engagement of the jaw clutch members after the desired speed synchronization has been achieved.
4. A transmission, as aforesaid, having a main shaft assembly possessing a minimum of inertia whereby to eliminate the need for synchronizers.
5. A transmission, as aforesaid, having the main shaft gears floatingly supported relative to the main shaft by a plurality of countershaft gears so as to minimize the inertia of the main shaft, and including clutch collars keyed to the main shaft for cooperation with the main shaft gears.
6. A transmission, as aforesaid, wherein the clutch collars are resiliently axially urged toward the respective main shaft gears, with the main shaft gears being axially shiftable for meshing engagement with their respective clutch collars, each gear and asscociated clutch collar being provided with conical cooperating faces disposed for engagement with one another prior to synchronization of the members whereupon the resilient means causes the clutch collar to meshingly engage the main shaft gear when the desired synchronization is achieved.
7. A transmission, as aforesaid, particularly having both a main transmission section and a range or auxiliary transmission section for increasing the number of speed ratios and including a single and continuous main shaft extending through both the main and range sections for minimizing the inertia and simplifying the ease and rapidity of shifting.
8. A transmission, as aforesaid, which permits shifting to occur without requiring depression of the clutch pedal and disconnection of the drive clutch, and which permits a vehicle, such as a truck, to be easily driven and shifted even by an inexperienced driver.
Other objects and purposes of the invention will be apparent to persons acquainted with devices of this type upon reading the following specification and inspecting the accompanying drawings.